import java.util.Arrays;
import java.util.Scanner;
import java.lang.Math;

public class practice {
    /*
       int[] arr = {1,2,3,4};
       for(int i=0;i<arr.length;i++){
           System.out.print(arr[i]+" ");
       }
       String s= Arrays.toString(arr);
       System.out.println(s);
       int[] ret= Arrays.copyOf(arr,arr.length);
       System.out.println(Arrays.toString(ret));
       int[] copy = new int[arr.length];
       System.arraycopy(arr,0,copy,0,arr.length);
       System.out.println(Arrays.toString(copy));
       int[] ret2=arr.clone();
       System.out.println(Arrays.toString(ret2));
   }
   public static void main1(String[] args) {//九九乘法表
       Scanner scanner=new Scanner(System.in);
       int n=scanner.nextInt();
       for(int i=1;i<=n;i++){
           for(int j=1;j<=i;j++){
               System.out.print(i+"*"+j+"="+i*j+" ");
           }
           System.out.println();
       }
   }


   public static void main(String[] args) {//开密码门
       int s= 123;
       System.out.println("输入密码");
       Scanner scanner= new Scanner(System.in);
       for(int i=0;i<3;i++) {
           int a = scanner.nextInt();
           if (a != s) {
               System.out.println("密码错误");
           } else if(a==s){
               System.out.println("芝麻开门");
           }
       }
   }


   public static void main(String[] args) {//判断二进制有几个1
       Scanner scanner= new Scanner(System.in);
       int a = scanner.nextInt();
       int n=0;
       for( n=0;a>0;a>>=1){
           n+=a&1;  //  n&n-1判断是不是2的次方;
       }
       System.out.println(n);
   }


   public static void main(String[] args) {//拿出二进制的奇位和偶数位
       Scanner scanner= new Scanner(System.in);
       int a = scanner.nextInt();
       int i;
       for(i=31;i>=0;i-=2){
           System.out.print((a>>i)&1);
       }
       System.out.println();
       for(i=30;i>=0;i-=2){
           System.out.print((a>>i)&1);
       }
   }


   public static void main(String[] args) {//公约数
       Scanner scanner= new Scanner(System.in);
       int a = scanner.nextInt();
       int b = scanner.nextInt();
       if(a<b){
           int temp=0;
           temp=a;
           a=b;
           b=temp;
       }
       int a1=a;
       int b1=b;
       int c=a%b;
       while (c!=0){
           a=b;
           b=c;
           c=a%b;
       }
       System.out.println("最大公约数为"+b);
       System.out.println("最小公倍数为"+a1*b1/b);
   }


   public static void main(String[] args) {//水仙花数
       for(int i=1;i<1000;i++){
           int sum=0;
           for(int j=10;j<=100;j*=10){
               sum+=(i/j)*(i%j);
           }
           if(sum==i){
               System.out.println(i);
           }
       }
   }


   public static void main(String[] args) {//水仙花数
       Scanner scanner=new Scanner(System.in);
       int num=scanner.nextInt();
       int count=0;
       int temp=num;
       int num1=num;
       while (num!=0){
           count++;
           num/=10;
       }
       int sum=0;
       while(temp!=0){
           sum+=Math.pow(temp%10,count);
           temp/=10;
       }
       if(sum==num1){
           System.out.println("ok");
       }
   }


   public static void main(String[] args) {//素数
       Scanner scanner=new Scanner(System.in);
       int num=scanner.nextInt();
       int i=2;
       while(i<num){
           if(num%i==0){
               System.out.println("不是素数");
               break;
           }
           else{
               i++;
           }
       }
       if(i==num){
           System.out.println(num+"是素数");
       }
   }


   public static void main(String[] args) {//判断素数
       int i,j;
       for( i=3;i<=100;i++){
           for(j=2;j<=100;j++){
               if(i%j==0){
                   break;
               }
           }
           if(j==i){
               System.out.println("素数是"+i);
           }
       }
   }


   public static void main(String[] args) {//判断闰年
       for(int year=1000;year<=2000;year++){
           if(((year%4==0)&&(year%100!=0))||year%400==0){
               System.out.print(year+" ");
           }
       }
   }


   public static int sum(int a, int b) {//方法名重载
       return a + b;
   }

   public static double sum(double a, double b) {
       return a + b;
   }

   public static double sum(int a, double b) {
       return a + b;
   }

   public static void main(String[] args) {
       System.out.println(sum(1, 2));
       System.out.println(sum(1, 1.44));
       System.out.println(sum(1.2, 1.3));
   }

   public static int func(int n) {//斐波那契数列
       if(n==1){
           return 1;
       }
       else  if(n==0){
           return 0;
       }
       return func(n-1)+func(n-2);
   }
   public static void main(String[] args) {
       System.out.println(func(3));
   }

   public static int sum(int n) {//递归打印123的每一位之和
       if(n<10){
           return n;
       }
       int temp=n%10+sum(n/10);
       return temp;
   }
   public static void main(String[] args) {
       System.out.println(sum(134));
   }

   public static void fun(int n) {//递归打印1234
       if(n<10){
           System.out.println(n);
           return ;
       }
       fun(n/10);
       System.out.println(n%10);
   }
   public static void main(String[] args){
       fun(1234);
   }


   public static int fun(int n) {  //求10以内的和
       if(n==1){
           return 1;
       }
       int temp=n+fun(n-1);
       return temp;
   }

   public static void main(String[] args) {
       System.out.println(fun(10));
   }


   public static int fun(int n) {//求n的阶乘
       if(n==1){
           return 1;
       }
       int temp=n*fun(n-1);
       return temp;
   }
   public static void main(String[] args) {
       System.out.println(fun(4));
   }


   public static int[] transform(int[] a) {//数组引用的指向
       for(int i=0;i<a.length;i++){
           a[i]=a[i]*2;
       }
       return a;
   }
   public static void main(String[] args) {
       Scanner input=new Scanner(System.in);
       int[] arr=new int[3];
       for(int i=0;i<arr.length;i++){
           arr[i]=input.nextInt();
       }
       //int[]arr2=arr;//引用的数组都具有一样的哈希值，指向的数据都一样会随之改变
       transform(arr);
       System.out.println(Arrays.toString(arr));
      //System.out.println(Arrays.toString(arr2));
   }

   public static void toString(int[] a){ //手动实现toString
       String str="[";
       for(int i=0;i<a.length;i++){
           str+=a[i];
       if(i!=a.length-1){
               str=str+","+" ";
           }
       }
       str+="]";
       System.out.println(str);
   }


   public static void main(String[] args) {   //实现数组/字符串的拷贝
       Scanner input=new Scanner(System.in);
       int[] arr=new int[3];
       for(int i=0;i<arr.length;i++){
           arr[i]=input.nextInt();
       }
       toString(arr);
       int[] arr2=arr.clone();
       int[] arr3=Arrays.copyOf(arr,arr.length);
       int[] arr4=new int[arr.length];
       System.arraycopy(arr,0,arr4,0,arr.length);
       System.out.println(Arrays.toString(arr));
       System.out.println(Arrays.toString(arr3));
       System.out.println(Arrays.toString(arr4));
   }

   public static void main(String[] args) {  //逆序数组
       int[]arr={1,2,3,4};
       int left =0;
       int right= arr.length-1;
       while(left<right){
           int temp=arr[left];
           arr[left]=arr[right];
           arr[right]=temp;
           left++;
           right--;
       }
       System.out.println(Arrays.toString(arr));
   }
    public static int binarySearch(int[] arr,int x) {  //二分查找
        int left=0;
        int right=arr.length-1;
        while (left<=right){
            int mid=(left+right)/2;
            if(arr[mid] <x){
                left=mid+1;
            }
            else if (arr[mid]==x){
                return mid;
            }
        }
        return -1;
    }

   public static void main(String[] args) {
       int[] arr={1,3,4,5,9};
       Arrays.sort(arr);
       int index=binarySearch(arr,5);
       if(index==-1){
           System.out.println("false");
       }
       else {
           System.out.println("find  "+index);
       }
   }


   public static boolean judge(int[] arr) { //判断是不是有序递增
       int left = 0;
       int right = arr.length - 1;
       while (left < right) {
           if (arr[left] <= arr[left + 1]) {
               left++;
           }
           else {
               return false;
           }
       }
           return true;
   }
   public static void main(String[] args) {
       int[] arr={1,2,3,5,5,7};
       System.out.println(judge(arr));
   }

   public static void main(String[] args) {   //冒泡排序
       int[] arr={1,3,5,2,75,7};
       for (int i=0;i<arr.length-1;i++){
           int flag=0;
           for(int j=0;j<arr.length-1-i;j++){
               if(arr[j]>arr[j+1]){
                   int temp=arr[j];
                   arr[j]=arr[j+1];
                   arr[j+1]=temp;
                   flag=1;
               }
           }
           if(flag==0){
               break;
           }
       }
       System.out.println(Arrays.toString(arr));
   }

   public static void main(String[] args) {  //找出数组中只出现一次的元素
       int[] arr={1,1,4,5,5};
       int flag=0;
       for(int x:arr){
           flag^=x;
       }
       System.out.println(flag);
   }

   public static void main(String[] args) {  //截取最后一个空格后的字符
       Scanner scanner =new Scanner(System.in);
       while(scanner.hasNextLine()){
           String str =scanner.nextLine();
           int index=str.lastIndexOf(" ");
           String str1=str.substring(index+1,str.length());
           System.out.println(str1);
           int len = str1.length();
           System.out.println(len);
       }

   }
    public static void main(String[] args) {  //找出只出现一次的字符
        int[]count =new int[256];
        String s="acd";
        for(int i=0;i<s.length();i++){
            count[s.charAt(i)]++;  //每个字符都对应一个数组下标 每放入相同的字符就加一
        }
        for(int i=0;i<s.length();i++){
            if(1==count[s.charAt(i)]){  //字符对应相同下标数组的值为一说明只出现一次
                System.out.println(s.charAt(i));
            }
        }

    }*/
    public static void main(String[] args) {  //找出只出现一次的字符
        Scanner scanner =new Scanner(System.in);
        String s = scanner.next();
        int[] count = new int[256];
        for (int i = 0; i < s.length(); i++) {
            count[s.charAt(i)]++;  //每个字符都对应一个数组下标 每放入相同的字符就加一
            if (1 == count[s.charAt(i)]) {  //字符对应相同下标数组的值为一说明只出现一次
                System.out.println(s.charAt(i));
            }
        }
    }
}
